Atomic layer deposition (ALD) of films is extensively used in the semiconductor industry for fabricating integrated circuits on semiconductor wafers. This technique is based on a binary chemical vapor deposition (CVD) reaction between two reactants introduced into a semiconductor processing chamber sequentially. The self-limiting surface reaction yields molecular or atomic layers of films in a controlled and conformal manner.
Tungsten plugs function as metal contacts in a semiconductor device or as electric conductors between upper and lower interconnect levels in a semiconductor integrated circuit. For example, tungsten plugs are used as metal contacts above the source/drain regions or above the gate stack in a complementary metal oxide semiconductor (CMOS) device.
In an ALD process for forming tungsten plugs, the binary reactants generally include a tungsten precursor in gas state such as tungsten hexafluoride (WF6) and a reducing gaseous reactant. The reducing gas is a hydrogen containing chemical such as B2H6 and Si2H6.
Poor quality such as absence of the plugs or non-uniformity of the deposited film in the desired areas can damage device structures and reduce the chip yield in the semiconductor fabrication. So deposition of a thin film in ALD of tungsten should be precisely controlled.